Re: Select only active entries

In response to Carel Combrink :
>
> They are not time stamped but in sequence. The latest active one is
> basically if  you look at number 5. It goes from active to inactive to
> active again at time of the query. I want to know if the last entry of
> ID 5 was active or inactive. And so-forth for all the rest of the
> ID's. So only select the IDs that were active on their last entry into
> the database.
>
> Is there a way of querying the data to obtain only the last entry in
> the table for a given ID?

There are no UPDATE or DELETE, just only INSERTs into the table?

If yes, maybe this should work for you:

test=*# select * from test_select;
 id | is_active
----+-----------
  5 | t
  5 | f
  6 | t
  7 | t
  8 | t
  5 | t
  8 | f
  9 | t
 10 | t
  6 | f
 10 | f
(11 rows)

test=*# select id, is_active from (select id, is_active, max(ctid), row_number() over (partition by id) from
test_selectgroup by id, is_active, ctid order by id, ctid desc) foo where is_active and row_number = 1; 
 id | is_active
----+-----------
  5 | t
  7 | t
  9 | t
(3 rows)


You *should* consider an additional column, timestamp for instance, the
trick with ctid isn't a clean solution.


Andreas
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Andreas Kretschmer
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